X-ray detectors for measuring X-ray radiation are typically implemented on the basis of the principle that the X-ray radiation is absorbed and a measurable signal is generated therefrom. The X-rays can be absorbed either by means of scintillators or by means of direct converters. In X-ray detectors comprising scintillators the X-ray quanta are converted into light by means of the scintillator and the light is measured by an array of photodiodes and converted into a measurable electrical signal. Photodiodes can be produced either on the basis of amorphous silicon which is arranged on a glass substrate or as what are referred to as active pixel sensors (APSs) on the basis of CMOS technology. CMOS photodiodes have certain advantages compared with other photodiodes (e.g. pixel sensors based on amorphous silicon); they consume less power, for example, and can be manufactured with a much smaller footprint and at considerably lower cost, as well as with additional integrated readout logic. However, they also have one disadvantage: X-ray radiation that has not been absorbed in the scintillator can be absorbed in the silicon substrate arranged underneath the CMOS photodiode and generate charges there which then diffuse into the photodiode and produce a strong noise signal there (referred to as a direct hit). Noise signals of this type are visible as a bright spot on an X-ray image and degrade the quality of the X-ray image, in particular in image sequences having a low X-ray dose (fluoro scene).